1. Field of the Invention
This invention relates to apparatus for measurement of natural gases in city gas metrology. Specifically this invention relates to an all-electronic utility gas metering using micro-machined silicon flow sensors or Micro Electro Mechanical Systems (MEMS) mass flow sensing technology to meter the city gas in the utility industry requiring custody transfer or tariff. This invention also provides the design and make of an all-electronic mass flow meter with remote data capability and other intelligent functions, which can be used to directly replace existing diaphragm gas meters for the utility industry without modification of the current installation schedules.
2. Description of the Related Art
Utility gas meters for city gas metering has been dominated b the mechanical diaphragm meters that have been invented some 170 years ago by a UK inventor, Thomas Glover. Since then, the materials that used to make the diaphragm gas meters have been improved, but the measurement principle and basic structure/configuration remain intact. The diaphragm meter measures the accumulated volumetric flowrate which is used for custody transfer or tariff bill to users. The beauty of this technology has been proven in its long history for its reliability and self-powered metering. However, the gas volumetric data are not constant against temperature and pressure variations. As the statistic consumption of the city gas will be about 5 times higher in winter compared to that, in summer, the city gas companies usually run a loss on the average and heavy government subsidy is often applied for the sustained operation of the city gas companies. There were since many efforts to improve the diaphragm meter technology in particular for solving the data dependence on temperature variations, e.g., D. E. Bruce and J. L. Esola, Temperature compensated gas meter, U.S. Pat. No. 4,538,458. However, the reliability and accuracy of those improvements had not been well proven and adopted for the field deployment. On the other side, the demands for networking or smart utility meters have led a number of efforts to add a mechanical data reader and electronic data converter for data relay. These efforts have not solved the basic requirements for gas data accuracy for custody transfer or tariff.
With the advancement of integrated circuitry industry, electronics gas meters have started to emerge. In mid-1980s, ultrasonic gas meters had been field tested and deployed in some European countries (see for example, W. Taphorn et al., Ultrasonic gas meter, U.S. Pat. No. 5,433,117). It has been hoped that the ultrasonic technology would be much easier to incorporate pressure and temperature sensors for better compensation of environmental variations on the gas metrology, but due to the cost and performance issues, the replacement of the mechanical meters has not been made possible as of today. Pearman et al. (A. N. J. Pearman et al, Electronic gas meter, U.S. Pat. No. 4,918,995) teaches an electronic gas meter using a MEMS mass flow sensor that shall have the automatic temperature and pressure compensation which further simplified the compensation scheme and reduced the cost for such. However, the construction and the electronics in the earlier 1990s were far more complicated to achieve the necessary metrology requirements. In addition, the MEMS sensor probe had its wire exposed to the detecting gas media which was prone to reliability issues. Matter (D. Matter et al., Increased accuracy gas energy meter, U.S. Pat. No. 7,222,028) proposed a new electronic gas meter with a MEMS mass flow sensor having an application specific integrated circuitry. The meter configured had the potential with a low cost because of the simplified electronics but the products based on this patent covered only a single utility gas meter model which made the application impractical. Muraoka et al. (Muraoka et al, Flowmeter, U.S. Pat. No. 7,861,585) disclosed an electronic gas meter with dual MEMS sensors for high flow rate utility gas measurement targeting users such as industrial applications, but due to the design with a high pressure drop, applications in city gas metrology could merely be realized. Nonetheless, the MEMS sensing technology based utility gas meters require far less components and can have a simple configuration that makes it possible to excel the current mechanical diaphragm utility gas meters with the desired enhancement in accuracy, adding advantages in electronic data safety, data management, and remote metering management, which could further be used for energy saving and conservation.
Jiang (C. Jiang et al., MEMS utility meters with exchangeable units, U.S. Pat. No. 8,994,552) and Yang (X. Yang et al, MEMS utility meters with, integrated. mass flow sensors, U.S. Pat. No. 9,109,935) have addressed the application requirements for utility gas applications for commercial and industrial users, but these designs could not be easily adopted for residential applications as the it is virtually impractical to alter the installation conditions for the vast numbers of the residential utility gas meters in the field. Filed installation of the special mechanical connectors shall not only be extremely costly but the often limited space at installation in the residential conditions shall not allow such operations. In addition, unlike the commercial and industrial gas metering applications, for the residential applications, the meters sometimes also require an integrated valve system that can be used to shut off the valve in case of emergency. The valve system shall also help for tariff management where the remote data or bill is not possible.
Therewith it is desired for this invention that a new design of MEMS based utility gas meter for residential applications shall be necessary. The new design shall be compatible in installation with the existing mechanical diaphragm meters for the practical deployment without having any impact to the meter metrology performance in line with the international utility gas metering standards while maintaining a similar mechanical connection configuration with the existing mechanical diaphragm meters such that the meters could be easily adopted in different field conditions.